1. Field of the Invention
The present invention is related to an automatic storage system, particularly to an automatic storage system that can store two articles arranged side by side in a depth direction of a shelf.
2. Description of the Related Art
An automatic storage system includes a rack having a plurality of shelves that can store articles, and a stacker crane that can transfer the article between the shelves and the stacker crane. A conventional automatic storage system has been known that can store two articles arranged side by side in a depth direction of a shelf (refer to Japanese Laid-open Patent Publication 2009-1380). In the conventional automatic storage system, a shelf includes a near-side storage portion and a far-side storage portion arranged side by side in the depth direction. The near-side storage portion is located facing a travelling path of the stacker crane.
In the conventional automatic storage system, a transfer device of the stacker crane is constituted by a slide fork that can extend and contract within a length wherein the slide fork can reach the far-side storage portion. Accordingly, this slide fork has an extension and contraction distance longer than that of the slide fork for storing one article. When transferring the article to or from the shelf, the transfer device extends the slide fork by a length of the far-side storage portion or by a length of the near-side storage portion in order to transfer the article. When unloading an article to a shelf by the slide fork as a transfer device, an elevator is stopped at an upper stop position wherein an article-placed surface of the slide fork is positioned higher than the shelf, and then the slide fork is extended. In this state, the elevator is lowered to a lower stop position so that the article is placed onto the shelf. When loading the article from the shelf, the elevator is stopped at a lower stop position wherein the article-placed surface of the slide fork is lower than the shelf, and then the slide fork is extended. In this state, the elevator is hoisted to the upper stop position so that the article is scooped up from the shelves and is placed onto the article-placed surface.
In the conventional automatic storage system having the far-side storage portion and the near-side storage portion, an extension and contraction distance of the transfer device is longer. Accordingly, depending on whether at the near-side storage portion or at the far-side storage portion, deflection amounts of the transfer device during extension thereof may be different from each other. As a result, in the conventional stacker crane, when unloading and loading the article, an upper position where the elevator is stopped higher than the shelf as a transport destination is set at a position higher than the shelf considering deflection when extending the slide fork to the far-side storage portion. Therefore, the lowering time when transferring the article from the upper stop position to the shelf becomes longer, so that the time when transferring the article becomes longer.